Page 86 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Musculoskeletal system: 1.3 The foot 61

VetBooks.ir 1.3 The foot

The foot as applied to the distal limb of a horse is important to know when the horse was last shod,
not an anatomical term supported by the Nomina how frequently it is shod and whether there have
Anatomica Veterinaria, but from common been any changes in the farriery management of the
usage it has evolved to mean that part of the horse that might be related to the onset of symptoms.
distal limb surrounded by the hoof and all the The nature of the hoof capsule precludes palpa-
structures contained within the hoof. The hoof tion and manipulation of the distal digit in the same
is the integument of the foot and is composed of manner as the rest of the limb, but many basic ele-
epidermis, dermis and subcutaneous tissue. The ments of the examination are similar. Examination
stratum corneum of the hoof epidermis forms of the foot with the horse at rest involves visual
the hoof capsule. The wall of the hoof capsule is inspection, palpation, application of hoof tes-
formed from three layers: the stratum externum, ters, paring the sole and manipulation of the digit.
which is derived from the limbic (perioplic) Visual inspection of the foot rapidly identifies gross
epidermis; the stratum medium, which is derived lesions such as hoof cracks or hoof-wall avulsions.
from the coronary epidermis and forms the bulk Additionally, the size of the foot in relation to the
of the thickness of the wall; and the stratum size of the horse, the shape of each foot and the
internum, which is thin and derived from the symmetry between the feet, and the relationship
parietal (lamellar) epidermis. between the foot and the limb are evaluated. More
The majority of the diseases of the foot subtle details such as the presence of flares and the
are secondary to infection or trauma and to circumferential patterns of the growth rings require
degeneration subsequent to recurrent low-grade closer observation. Palpation of the foot is the most
trauma. Trauma to structures of the foot is practical way to determine if the foot is excessively
primarily related to its proximity and interaction warm, to identify soft areas in the sole and also to
with the ground and internal stresses associated identify moistness, particularly at the hairline, that
with exercise. Infection follows surface was not identified on visual inspection. Paring of the
contamination, penetration of the integument sole, best performed without a shoe on the foot, will
through injury or, rarely, haematogenous spread. expose bruises and defects in the sole. Application of
hoof testers elicits a withdrawal response when they
CLINICAL PRESENTATION are positioned over a focus of pain; however, this
cannot be used to infer which of the tissues between
The most common presenting symptom for dis- their jaws is affected. Manipulation of the limb by
eases affecting the horse’s foot is lameness, usually flexion, extension and rotation of the distal limb will
caused by a focus of pain or, much less frequently, by determine restriction in range of motion and elicit
a mechanical change in function. In more chronic a withdrawal response if structures associated with
cases the foot may present with a change in appear- such motion are inflamed.
ance, shape or size. Diseases of the foot are the most There are no characteristics of gait that conclu-
common cause of lameness in the forelimbs. In the sively identify lameness arising from the foot. Horses
hindlimbs they are generally considered less com- with bilateral disease frequently present with a stiff
mon than diseases affecting the hock and fetlock and short-striding gait, which in conjunction with
joints, although this may lead to underdiagnosis. the known incidence of diseases in the forefeet and
The signalment is unlikely to be specific, but it the signalment are highly suggestive. The exception
is useful to compare it with the history and clinical is the severely and acutely laminitic horse, whose
signs when considering the likelihood of a specific extremely stilted gait is almost pathognomonic, par-
diagnosis. The history for horses presenting with ticularly when associated with a shifting of weight
a disease affecting the foot is very variable. It is from the forequarters to the hindquarters.